The modifiability of characters important in potato breeding

About 2,600 potato clones of 29 combinations were repeatedly analyzed for some years at a stretch in order to determine the degree of modifiability of both a large number of separate characters and the general impression of underground plant parts on lifting in an early stage, in the mature condition and on assessing tuber samples.The ultimate aim of these investigations was to find out how far strictness is justified when selection is applied in breeding new potato varieties. Therefore correlations between the clonal generations were calculated from the data obtained for the various characters and the general impression. Only those characters for which these correlations are positive and high, i.e. slightly modifiable characters, can be strictly selected. Flesh colour appeared to be slightly modifiable. This also applies to tuber shape and maturity though these characters are somewhat more modifiable. Considerably to even strongly modifiable are eye depth, stolon length, under water weight and sprout length. Foliage type, stolon number, date of emergence and degree of common scab affection are extremely modifiable. The same is true for the general impression in the three stages mentioned above.As the general impression, in which the various separate characters and such characters as tuber number, size and yield are included, is initially decisive as to retention, it cannot but be concluded on the ground of the results obtained by others and the author that on a strict selection the major part of the most valuable individuals will be lost. This can be avoided if the negative selection takes the place of the positive in the first stages, i.e. instead of retaining only the apparently good ones the very poorest clones should be discarded in every selection stage. Not until the number of tubers suffice to lay out statistically justified tests can a change be made from the negative to the positive selection.     

Utilisation of the Commonwealth Potato Collection in potato breeding

Summary The use of the Commonwealth Potato Collection in potato breeding is set in the context of the evolution of the crop and the need to widen its genetic base by introgression and base broadening. The introduction of the potato to Europe and its subsequent worldwide spread is described. An introduction is given to the world's major potato genebanks, and the current status of the Commonwealth Potato Collection is presented. Material from this genebank has been extensively used to improve the potato. Work on wild species as sources of resistance to late blight started before the genebank was initiated, and since then CPC accessions have provided major R-genes and durable resistance to breeders, greatly benefiting growers and consumers of the potato. Progress identifying and exploiting resistance to viruses and potato cyst nematodes is described. New sources of further pest and disease resistance genes are present in the germplasm in the collection, offering the potential to overcome current and future pests and diseases. Use of the cultivated species in the collection for base broadening is described and discussed. The collection also harbours a wide range of quality traits of use to breeders, including variation for cooking and crisping, anthocyanins, carotenoids, ascorbate metabolism and others. As breeding and genetics become more precise, and as both the knowledge of biochemical pathways and means of analysing chemical composition advance, new ways of accessing this variation become possible. Possible strategies to achieve these goals are discussed.     

Some data and figures on potato breeding in the Netherlands

Summary The rapid growth of the number of potato breeders in the Netherlands was favourably influenced by a wide spread interest for all problems concerned with potatoes, by financial support and advice.In 1954, the number of potato breeders was 193; 46 of them can be considered professional breeders, while of 20 breeders one or more varieties figure in the Dutch List of Varieties 1954.The creation of the Foundation for Agricultural Plant Breeding resulted in the enhancement of the level of potato breeding and the increase of the number of potato seedlings raised every year.     

Phenotyping early blight resistance in potato cultivars and breeding clones

Thirty-two potato cultivars/clones were evaluated for resistance to early blight using different methods. The evaluations were performed under field and greenhouse conditions. In the field experiments, plants were evaluated for disease symptoms, and the relative area under the disease progress curve and percent defoliation were determined. In the greenhouse experiments, leaf lesion sizes were determined on either intact plants or detached leaves after drop inoculation with Alternaria solani. The effect of leaf position (lower, middle or upper part of the plant) on lesion size was investigated. There was no correlation between lesion sizes on lower leaves and upper leaves after inoculation. However, significant correlations between lesion sizes on lower and middle leaves and also between middle and upper leaves were found. Furthermore, we found significant correlation between the results of resistance studies in the field and in intact plant inoculation experiments in the greenhouse. In contrast, results from the detached-leaf experiment were not correlated with either greenhouse intact plant tests or field results. The results indicate that using detached-leaf assays for screening potato for early blight resistance is not accurate. We found significant differences in resistance to A. solani among cultivars/clones in both the field and in greenhouse experiments.     

Reciprocal effects in true potato seed breeding in short-day length environments

Reciprocal crosses may have significantly distinct performances regarding tuber characteristics in potato, suggesting the importance of cytoplasmic effects in this crop. The selection of parents for true potato seed breeding therefore needs to consider this potential effect when determining the direction of a cross. The aim of this research was to determine whether a broad‐based true potato seed breeding population, developed at the Centro Internacional de la Papa, could be affected by cytoplasmic effects in the short‐day length environments of the tropics. Two random sets of reciprocal biparental crosses were included in the first set of experiments, which were grown in two contrasting Peruvian locations. Only one out of 14 reciprocal crosses showed significantly distinct performance for tuber yield and tuber set. In the second set, only one of each of the 12 reciprocal crosses had distinct performance for vine earliness, days to flowering and flowering intensity, but four of the reciprocal crosses in the second set showed distinct pollen production. The results suggest that cytoplasmic effects in this breeding population are more important for reproductive characteristics such as pollen production than for tuber yield. This finding is not surprising because male sterility in potato results from the interaction between sensitive cytoplasm and dominant nuclear genes.     

Coagulable protein in potato: Screening method and prospects for breeding

Summary From tubers of 34 varieties of Solanum tuberosum, extracts were prepared and analysed for crude protein and coagulable protein by the Kjeldahl method. Content of coagulable protein was 0.37–1.24%. From the same material, juice was prepared with a juice centrifuge and analysed for coagulable protein by the Kjeldahl and microbiuret method. The average amount of coagulable protein in the juice was 81.8% of the total coagulable protein. The correlation coefficient between coagulable protein in the juice and total coagulable protein was 0.956. The correlation coefficient between Kjeldahl and microbiuret data for coagulable protein in the juice was 0.956. Analysis of tuber juice by the microbiuret method is recommended as a rapid screening technique for coagulable protein.Relationships between protein data of the 34 varieties and earliness, yield and content of dry matter were analysed statistically. Content of coagulable protein in fresh material correlated with content of dry matter (rs=–0.756), yield of fresh potatoes (r=–0.615) and earliness (r=–0.361) but not significantly with yield of dry matter (rs=–0.309). Coagulable protein in dry matter correlated with fresh yield (r=–0.525), but not significantly with content of dry matter (r=–0.260), yield of dry matter (r=–0.131) and earliness (r=–0.054). Path coefficient analysis showed that 67% of the variation in coagulable protein in fresh material was statistically determined by earliness, content of dry matter, fresh yield and content of uncoagulable protein in fresh material, whereas only 34% of the variation in content of coagulable protein in dry matter was determined by these components. A high content of coagulable protein in fresh or dry matter can be combined with early maturity and with high yield of dry matter. Coagulable protein in dry matter seems to be a more suitable criterion of selection than coagulable protein in fresh material.     

Investigation of long-term field experiments on response of breeding lines to common scab in a potato breeding program

Common scab, caused by Streptomyces scabies, is a disease that produces scab-like surface lesions on potato tubers. Testing for susceptibility/resistance of breeding lines at the Potato Research Centre of Agriculture & Agri-Food Canada (AFC) is carried out in a scab nursery maintained at AFC for the annual scab evaluation field trials. A replicated field trial routinely consists of breeding lines from previous testing season(s) plus newly selected lines. Data of scab scores generated from long-term experiments thus formulate an incomplete 2-way table over combinations of breeding lines (genotypes) and trials (years). This requires an advanced statistical method to estimate genetic parameters for evaluation purposes. A data base with 1,435 scab index scores from 344 breeding lines were extracted from 5 years (1995–1999) of field experiments in the scab nursery maintained at AFC. The statistical method Residual Maximum Likelihood (REML) was employed to estimate variance components of the breeding population and Best Linear Unbiased Predictor (BLUP) was used to predict genetic merit of breeding lines. High heritability was obtained from variance components estimated by REML. The BLUP scores of breeding lines provided reliable evaluation of their responses to common scab. Two data base sub-sets were separately formulated from the original data base for those parents and grandparents of the breeding lines having pedigree records available. They were again subjected to REML and BLUP analyses to compare the responses to common scab and identify sources of resistance at the parental and grandparental levels. Two random data sets with equal sized samples of breeding lines were also generated from the over-all data base. The two sets of BLUP scores between corresponding breeding lines and parents showed high association which provides an assessment of the validity of the evaluation process.     

Variation in pathogenicity of the potato root eelworm (Heterodera rostochiensis woll.,) and its significance in potato breeding

Summary Breeding for resistance to Heterodera rostochiensis was started in Scotland in 1952, using certain clones of Solanum tuberosum subsp. andigena as the source of resistance. Resistance was manifest by the almost complete failure of larvae to mature in the roots of resistant seedlings, particularly those derived from the clone C.P.C.1673.In 1955 an eelworm population was found which overcame this resistance and was, for this reason, designated as aggressive.Resistance was also overcome in selfed and hybrid seedlings derived from subsp. andigena C.P.C. 1685 and C.P.C.1690. Resistance in Solanum vernei was apparently maintained against the aggressive eelworm population which was studied. This aggressive eelworm population multiplied normally on commercial potato varieties.In a first survey of Potato Root eelworm infested soils in Britain about 10 per cent of the eelworm populations sampled were found to differentiate little or no resistance in a test plant which was at least simplex for a resistance factor H, derived from C.P.C. 1673.

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Hiermede wordt hetzelfde bedoeld als met S. andigenum.     

Identifying superior parents in a potato breeding program using cross prediction techniques

Cross prediction techniques were applied to data collected from over 600 hybrid combinations of potato (Solanum tuberosum) and analyzed to determine the potential of using early generation cross prediction techniques to identify superior parental clones. Performance of parental lines based on parameters collected in early generations were compared with the observed frequencies of desirable recombinants with a common parent in the latter stages of a breeding program. Results showed that value of parents, in their ability to produce desirable recombinants in breeding programs, can be predicted using univariate cross prediction techniques. This type of information can be available from early generation progeny trials and could easily be incorporated into a practical potato breeding scheme. This revised version was published online in August 2006 with corrections to the Cover Date.     

Combining ability analysis and correlation between breeding values in true potato seed

True potato seed (TPS) requires the selection of appropriate parents for developing hybrid offspring. Parents for routine crossing schemes need to be selected according to their combining ability. Hierarchical and factorial mating designs provide a mean values to assess the general combining ability (GCA) of clones included in crossing schemes. Furthermore, specific combining ability (SCA) may be investigated using the factorial mating design. The aim of this research was to determine the combining ability of clones included in early and intermediate TPS breeding populations developed by the Centro Internacional de la Papa (CIP). Likewise, correlations between breeding values (or additive genetic correlation, p_A) were calculated. Two hierarchical mating designs (in both the early and intermediate populations) and one factorial mating design (in the intermediate population) were evaluated in two contrasting Peruvian locations (La Molina ‐ coastal desert, and San Ramon, warm humid tropics). Plant and tuber characteristics were recorded in these experiments. Significant GCA was observed for tuber yield in all experiments. The male's p_A between plant vigour after transplanting and tuber yield was significant, thereby suggesting that offspring with early vigorous growth are high yielding. Plant vigour was also correlated with tuber set, but only among the breeding value of female parents, which suggests that high tuber yield could be achieved because offspring with early, vigorous growth have many tubers. High tuber yielding hybrids can be obtained by choosing parents with significant GCA, whose tuber yield can also be further enhanced if the crosses have a significant SCA.     

Significance of wild species and primitive forms for potato breeding

Three stages in the history of the utilization of wild potatoes are outlined, and it is suggested that we are now entering on a fourth stage, typified by a fuller international co-operation than has hitherto been possible.The availability of useful genes is considered in the light of our knowledge of the crossability and evolutionary relationships of potato species. Breeding mechanisms in species at various levels of ploidy are shown to play an important part in speciation, and the significant role of asexual reproduction in potatoes is discussed.The geographical localization of most genes carrying resistance to Phytophthora, viruses, Heterodera, Leptinotarsa and frost is discussed. Certain explanations to account for this localization are put forward.Samenvatting Drie stadia in de geschiedenis van het gebruik van wilde aardappelsoorten en primitieve aardappelrassen worden genoemd. Omstreeks 100 jaar geleden waren nieuwe rassen nodig ter bestrijding van degeneratieziekten, terwijl omstreeks 1909 het wilde materiaal voor het kweken op ziekteresistentie ter hand werd genomen. Het 3e stadium begon in 1925 toen de eerste grote expeditie werd gehouden om materiaal te verzamelen voor een onderzoek naar de genetische variatie van de aardappelsoorten. Thans is men gekomen in het 4e stadium, nl. een nauwere internationale samenwerking dan tot nu toe mogelijk was.Schrijver geeft een overzicht van de perspectieven voor het kweken op resistentie tegen Phytophthora, virusziekten, Heterodera, coloradokever en vorst. Het is gebleken dat bepaalde genen in bepaalde gebieden voorkomen (geographical localization).

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Zusammenfassung Bedeutung der Wildkartoffeln und Primitivformen für die Kartoffelzüchtung In der Geschichte der Verwertung der Wildkartoffeln werden drei Stufen abgezeichnet und die Ansicht vertreten, daß wir eben in eine vierte eintreten, welch durch vollere internationale Zusammenarbeit als bisher möglich gewesen ist, charakterisiert wird.Die Tatsache, daß wertvolle Gene zur Verfügung stehen, wird im Lichte unserer Kenntnisse der Kreuzbarkeit und der Entwicklungsbeziehungen von Kartoffelarten betrachtet.Es wird aufgezeigt, daß Reproduktionsmechanismen in Arten auf verschiedenen Stufen der Ploidie eine wichtige Rolle in der Artzüchtung spielen, ferner wird die wichtige Rolle asexueller Reproduktion in Kartoffeln behandelt.Die geographische Lokalisierung der meisten Genen, die gegen Phytophthora, Viren, Heterodera, Leptinotarsa und Frost resistent sind, ist hier behandelt. Erklärungen für diese Lokalisierung werden hier vorgeschlagen.Zusammenfassung In der Geschichte der Verwertung der Wildkartoffeln werden drei Stufen abgezeichnet und die Ansicht vertreten, daß wir eben in eine vierte eintreten, welche durch vollere internationale Zusammenarbeit als bisher möglich gewesen ist, charakterisiert wird.Die Tatsache, daß wertvolle Gene zur Verfügung stehen, wird im Lichte unserer Kenntnisse der Kreuzbarkeit und der Entwicklungsbeziehungen von Kartoffelarten betrachtet.Es wird aufgezeigt, daß Reproduktionsmechanismen in Arten auf verschiedenen Stufen der Ploidie eine wichtige Rolle in der Artzüchtung spielen, ferner wird die wichtige Rolle asexueller Reproduktion in Kartoffeln behandelt.Die geographische Lokalisierung der meisten Genen, die gegen Phytophthora, Viren, Heterodera, Leptinotarsa und Frost resistent sind, ist hier behandelt. Erklärungen für diese Lokalisierung werden hier vorgeschlagen.

     

A breeding method for accelerated development of cold chipping clones in potato

Summary The development of potato cultivars having acceptable chipping quality after cold storage is important because it reduces costs to growers while ensuring continuity of supply to processors throughout the year. Over 5100 single-hill progenies were planted to select for cold chippers. A breeding procedure for selecting and evaluating these progenies for cold chipping ability was used, and 38 desirable genotypes were identified. These selections were increased in the second clonal generation and evaluated for yield, specific gravity, and seven chipping treatments of varying storage duration/temperature/reconditioning duration and were compared to standard chipping cultivars Atlantic, Monona, Norchip, and Snowden. Twenty-two selections yielded Norchip the highest yielding cultivar, while 15 selections had a specific gravity Atlantic, the highest specific gravity cultivar. Snowden was the best chipping cultivar overall and some selections were not significantly different than Snowden. Overall, nine selections combined high yield and specific gravity with the ability to produce attractive chips from 4° C. Single-hill selection for cold chipping could potentially save four years in the breeding process by the identification of good parents, the recycling of good parental cross combinations, and the evaluation of progeny for chipping earlier in the breeding program.     

The use of adventitious buds to prevent chimerism in mutation breeding of potato

Summary Investigations are described to reduce chimerism by means of adventitious buds. Adventitious buds were obtained from tuber slices that had been rooted by auxin. Mutagenic treatments were applied at different stages previous to the development of adventitious buds. Mutations were induced by ethyl methanesulphonate (EMS) and X-rays. The use of the adventitious-bud technique resulted in a considerable reduction of chimerism when X-rays were used, but not so with EMS. A dose of 2 krad of X-rays was optimal for the production high numbers of mutated plants. With higher doses rooting of slices and bud formation were inhibited.     

Combining ability and correlations for yield components in early generations of potato breeding

A partial diallel set of crosses was made between 14 potato cultivars chosen for their fertility, from those included in a potato breeding programme at the NEIKER – Basque Institute for Agricultural Research. The progeny were grown in completely randomized trials from 1997 to 1999. Performance for yield, tuber number and average tuber weight was analysed in seedling and two clonal generations. Variance estimates due to both general combining ability (GCA) and specific combining ability (SCA) were significant in all generations for all traits under study. However, SCA was more important than GCA in almost all cases. Correlation coefficients among characters, generations, GCA and SCA effects were examined. For tuber yield no relation was obtained between generations; however, average tuber weight and yield were positively associated in all generations. The results indicate that appropriate selection criteria depend strongly on the particular cross. The implication for a breeding strategy are discussed.     

An evaluation of Solanum verrucosum Schlechtd. For its possible use in potato breeding

Summary Solanum verrucosum is a diploid (2n=24) wild potato species from Mexico. It is self-compatible, but in greenhouse artificial selfing is mostly necessary for seed setting. The species has a good male and female fertility and possesses resistance to different races and isolates of Phytophthora infestans. It is easily crossable with different species from South America. The good crossability, the genomic constitution and resistance to diseases favour its use in potato breeding at the diploid level.     

Selection for verticillium wilt resistance in potato breeding populations derived from four cross types

Verticillium wilt (VW) is one of the important yield-limiting diseases for potato production. To develop resistant clones, the potential for early generation selection was studied using three basic selection methods, individual, family, and within family selection, for two clonal generations. A total of 152 clones were derived from four cross types (2x × 2x, 2x × 4x, 4x × 2x and 4x × 4x). Clones were evaluated for maturity, symptom expression, yield and stem colonization in replicated trials. Heritability and selection response for the traits were estimated for each selection method. Direct selection in the second clonal generation and individual selection showed more gain than that from other methods. Both 2x × 2x and 4x × 2x families were higher yielding and had lower stem colonization scores than 2x × 4x and 4x × 4x crosses. Therefore, 2x × 2x or 4x × 2x crosses between carefully chosen parents with high yield and VW resistance may produce offspring with superior performance.     

Selection for cold chipping genotypes from three early generations in a potato breeding program

Chipping potatoes are an important market for the processing industry. Of the traits influencing chip quality,chip color is market limiting since other traits have diminished value without light chip color. Cold (4 ^°C) storage can reduce storage losses and cultivars producing light colored chips directly from cold storage are needed for this reason. Selection for cold chipping cultivars is traditionally practiced by visual evaluation of progeny the first few years in the field, followed by selection for cold chipping in years 4–5. Early generation selection for cold chipping may reduce cultivar development time by identifying good chipping progeny, families and parents earlier in the breeding cycle. Progeny from 175 4x × 4x families were evaluated from three early generations. They were greenhouse grown tubers (GGT) evaluated after6 mo. storage using randomly selected progeny, and field grown single hills propagated from either seedling transplants (FTR), or from greenhouse grown tubers (FGT). Progeny from field grown generations were selected first by visual evaluation, and then by random selection and chipped after6 mo. (visual selections) or 3 and 6 mo. storage (random selections). Cold chipping progenies were found in all three early generations. The earliest generations for selection are GGT or FTR, but may be less efficient than FGT. Correlations suggest that reliable parent and family selection is possible using GGT data. Visual selection eliminated 4/5 of the good chipping progeny, while identifying 8 of 11,714 genotypes combining visual merit and cold chipping potential. Increased genetic variation and sexual polyploidization are possible strategies for increasing the number of desirable genotypes. This revised version was published online in August 2006 with corrections to the Cover Date.